Abstract:
Many of our container-grown ornamental shrubs are produced within 15 months from the cutting up to saleable size. Therefore these mass-produced plants are rather cheap and production costs have to be kept at a minimum. One of the main cost factors is a repeated feeding by hand. It is impossible to give all the fertilizer the needs during the growing season because of the high salt concentration on the one side and the leaching of nutrients on the other. And liquid fertilizers raise problems too, especially in very wet years. To avoid these problems the fertilizer industry offers various slow-release fertilizers. They are based on two different principles; one is to condense urea with different aldehydes (Ureaform, Crotudor, Isodur); the other is to coat a soluble fertilizer with a material that releases the nutrients slowly.

But up till now only few investigations are published on questions like the following: in which amount should these fertilizers be given to grow containerized